Process for the production of liquid oxygen by separation from air



March 19, 1957 R. BECKER 2,785,548

PROCESS FOR THE PRODUCTION OF LIQUID OXYGEN BY SEPARATION FROM AIR Filed May 20, 1955 3 Sheets-Sheet 1 March 19, 1957 R. BECKER PROCESS FOR THE (PRODUCTION OF LIQUID OXYGEN BY SEPARATION FROM AIR 3 Sheets-Sheet 2 Filed May 20, 1955 March 19, 1957 R BECKER 2 785,548

. PROCESS FOR THE PRODUCTION OF LIQUID OXYGEN BY SEPARATION FROM AIR Filed May 20, 1955 3 Sheets-Sheet 3 PROCESS FOR THE PRODUCTION OF LIQUID OXYGEN BY SEPARATION FROM AIR Rudolf Becker, Munchen-Solln, Germany, assignor to Gesellschaft fur Lindes Eismaschinen Alttiengcsellschaft, Munich, Germany Application May 20, 1955, Serial No. 509,761

(Ilaiims priority, application Germany May 26, 1954 8 Claims. (Cl. 62175.5)

This invention rel-ates to a process for the production of liquid oxygen by separation from air.

Various processes for this purpose have already been disclosed. In these known processes, highly compressed air is employed. In view of the large amounts of cold required (owing to the extraction of the oxygen in liquid form), the compressed air is cooled by a work-performing expansion or by a simple throttle expansion in which the Joule-Thomson effect is utilised.

It is an object of the invention to provide a new and improved process for the production of liquid oxygen, in

which low-pressure air is employed in combination'with a nitrogen refrigerating circuit. Favourable consumption figures and a particularly simple, readily operable arrangernent are the advantages afforded by the new process.

According to the invention, there is provided a process for the production of liquid oxygen by separation from air, comprising the steps of compressing the air to a uniform pressure of about 5 to 6 atmospheres, cooling the compressed air in air regenerators in heat-exchange with nitrogen coolant produced in the air separation, separating the air into oxygen and nitrogen in a two-stage air separator, extracting nitrogen at about 5 atmospheres pressure from the top end of the high-pressure stage of the separator, heating the extracted nitrogen in said air regenerators in heat-exchange with the air passing through the latter, further compressing the heated nitrogen in a nitrogen-compressor to a pressure of about 16 to 30 atmospheres, cooling the high-pressure nitrogen in nitrogen regenerators in heat-exchange with cold, expanded nitrogen, branching off a portion of the cooled, high-pressure nitrogen at an intermediate position on the nitrogen regenerators, expanding the last-mentioned nitrogen by allowing the same to lose energy mechanically, to-a pressure substantially equal to that in said high-pressure stage, thereby to obtain said cooled, expanded nitrogen, re-heating the cold, expanded nitrogen in the nitrogen regenerators and thereafter drawing the latter back into the nitrogen compressor to be re-circulated, supercooling the more highly cooled remainder of the nitrogen leaving said nitrogen regenerators, in heat-exchange with said cold, expanded nitrogen, and supplying the supercooled nitrogen to the low-pressure stage of the air-separator at a location near to the top thereof, extracting said nitrogen coolant from the top of said low-pressure stage, and extracting substantially pure oxygen from the bottom of the latter stage.

The cold output obtained by the latter arrangement may be increased by branching oil? a part-of the nitrogen from the high-pressure stage, preheating the derived nitrogen, subjecting the latter to a work-performing expansion, and combining the expanded gases with the nitrogen leaving the low pressure stage.

Instead of expanding nitrogen from the high-pressure stage, part of the air from the high-pressure column may be preheated, subjected to a work-performing expansion, and returned to the low-pressure stage.

The oxygen produced by this process is obtained in subnite States Patent O stantially pure form and in very good yields and the regulation of the cold required is simply effected by regulation of the nitrogen circuit in which the nitrogen produced provides the replacement nitrogen for the nitrogen refrigerating circuit.

For a better understanding of the invention and to show how the same is to be carried into effect, reference will now be made to the accompanying drawing, in which Figure 1 represents diagrammatically one constructional form of an apparatus for the production of liquid oxygen, and Figures 2 and 3 represent two other such constructional forms similar to that of Figure 1. Referring firstly to Figure l the air to be separated is compressed to an absolute pressure of approximately 5.5 atmospheres in a compressor 1, After dissipation of its heat of compression in a cooler 2, the compressed air is led through a regenerator 3 to a two-stage air-separator 5, 6 and is introduced at 12 into the lower column 5 of the separator. The cooled, compressed air is separated in the latter into impure oxygen and pure nitrogen. The former is extracted in liquid form at 15, is supercooled in a heatexchanger 9 in heat-exchange with expanded nitrogen taken at 7 from the upper column 6 of the separator at an absolute pressure of about 1.2 atmospheres, expanded through a valve 26 to the pressure of the upper column 6 and introduced into the latter at an intermediate position.

The nitrogen extracted in gaseous form from the top of I compressed in a turbo-compressor 16 to a pressure of,-

for example, about 16 atmospheres. The other part of the nitrogen is led through a duct 31 and combined at 32 with the first part which has been expanded again to about 5 atmospheres absolute pressure in a turbine 20. The nitrogen which is compressed to about 16 atmospheres absolute pressure is caused to give up its heat of compression in a water-cooler 34 and is thereafter passed through one of two nitrogen regenerators 21, 22, i. e. 21.

A portion of this highly compressed nitrogen is branched 01f at 18 before being completely cooled and is expanded in the turbine 20 to an absolute pressure of about 5 atmospheres. After expansion at 32, this portion is combined with the other part of the nitrogen taken from the lower column 5. The combined stream of nitrogen gives up its surplus cold in a heat-exchanger 17 to unexpanded nitrogen, which is thereby liquefied or supercooled, and is returneed through the other of the two nitrogen regenerators 21, 22, i. e. 22, to the intake duct of the turbo-compressor 16. The remainder of the nitrogen is passed through theentire length of the regenerator 21, is combined at 24 with the above nitrogen portion after any liquid already formed has been removed in a nitrogen separator 23 and is expanded together with this portion in the turbine 20. The liquid fraction removed from the compressed nitrogen in the separator 23 is supercooled in the heat-exchanger 17 and in the exchanger 10 (or liquefied if no liquid has yet been separated off in the regenerator) and thereafter expanded in a valve 28 and introduced at S into the upper column 6 of the air separator. In addition, nitrogen liquefied in the lower column 5 is also fed at 8 to the upper column 6 after extraction at 11 from the lower column, supercooling in the exchanger 10 and expansion in a valve 27. Liquid oxygen obtained in the upper column 6 is extracted through a valve 29 and fed to its place of use. Gaseous nitrogen taken from the top of the upper column 6 at 7 gives up its surplus cold in the exchangers 10 and 9 to the nitrogen and oxygen liquids to be cooled and enters the Patented Mar. .19, 1957 atmosphere by way of the loose mass of the regenerator 4 in the direction of the unbroken arrows.

Both the air regenerators 3 and 4 and the nitrogen regenerators 21 and 22 are changed over at particular in tervals of time. Thus, after the change-over, the air to be separated passes through the regenerator 4 into the apparatus, whilst the nitrogen produced escapes through the regenerator 3 (chain-lined arrows). Similarly, the compressed nitrogen is cooled by the regenerator 22 and the cold nitrogen expanded to 5 atmospheres absolute pressure is reheated by the regenerator 21 and passed to the intake duct of the compressor 16. The incompletely cooled nitrogen is extracted from the regenerator 22 at 19 after the change-over of an automatically actuated valve 25 and flows to the expansion turbine 29. The regenerators are provided at their upper hot ends with automatically changed-over valves, and at their lower cold ends with automatically acting non-return valves. A nonreturn valve 33 connected between the heat-exchangers 13, 14 and the compressor 16 prevents reactions of the change-over impulses on the lower column 5.

Referring now to Figure 2, part of the nitrogen taken from the lower column 5 and branched off at 39 is branched off at 42, preheated in a heater 35, subjected to a work performingexpansion, and fed back at 37 into the duct for the nitrogen leaving the upper column 6 at 7.

Referring now to Figure 3, instead of expanding nitrogen from the column, a part of the air may be extracted, for example, from the pressure column at 38 through a duct 39, subjected to a work-performing expansion in the turbine 36 after preheating in the heater 35 and returned to the centre of the upper column 6 at 41 through the duct 40.

We claim:

1. A process for the production of liquid oxygen by separation from air, comprising the steps of compressing the air to a uniform pressure of about 5 to 6 atmospheres, cooling the compressed air in air regenerators in heatexchange with nitrogen coolant produced in the air separation, separating the air into oxygen and nitrogen in a two-stage air separator, extracting nitrogen at about 5 atmospheres pressure from the top end of the high-pressure stage of the separator, heating the extracted nitrogen in said air regenerators in heat-exchange with. the air passing through the latter, further compressing the heated nitrogen in a nitrogen compressor to a pressure of about 16 to 30' atmospheres, cooling the high-pressure nitrogen in nitrogen regenerators in heat-exchange with cold, expanded nitrogen, branching off a portion of the cooled, high-pressure nitrogen at an intermediate position on the nitrogen regenerators, expanding the last-mentioned nitrogen by allowing the same to lose energy mechanically, to a pressure substantially equal to that in said high-pressure stage, thereby to obtain said cooled, expanded nitrogen, reheating the cooled, expanded nitrogen in the nitrogen regenerators, and thereafter drawing the latter back into the nitrogen compressor to be recirculated, super-cooling the more highly cooled remainder of the nitrogen leaving said nitrogen regenerators in heat-exchange with said cold, expanded nitrogen, and supplying the supercooled nitrogen to the low-pressure stage of the air-separator at a location near to the top thereof, extracting said nitrogen coolant from the top of said low-pressure stage, and extracting substantially pure oxygen from the bottom of the latter stage.

2. A process according to claim 1, and comprising the further step of branching ofi a portion of the nitrogen extracted from the high-pressure stage of the air separator and combining said portion with the nitrogen which has been subjected to an expansion in which energy is mechanically lost.

3. A process according to claim 1, and comprising the further step of branching off a portion of said remainder in a nitrogen separator before the supercooling operation and combining said portion with the nitrogen being subjected to an expansion in which energy is mechanically lost.

4. A process according to claim 1, and comprising the further steps of extracting impure oxygen from the bottom of said high-pressure stage, and feeding said impure oxygen to said low-pressure stage at a position intermediate the ends of the latter.

5. A process according to claim 4, and comprising the further step of separately cooling the nitrogen fedto the air separator and the impure oxygen fed from the high to the low-pressure stage of said separator in heat-exchange with said nitrogen coolant.

6. Process according to claim 1, and comprising the further step of extracting the nitrogen to be subjected to an expansion in which energy is mechanically lost from relatively warm locations in the nitrogen regenerators.

7. A process according to claim 1, and comprising the further steps of branching off a portion of the extracted nitrogen, dividing said portion into two parts, combining one part with the nitrogen which has been subjected to an expansion in which energy is lost mechanically, subjecting the other part to a further expansion in which energy is lost mechanically, and combining said other part with said nitrogen. coolant.

8. Process according to claim 1, and comprising the further steps of extracting a portion of the air that is being separated at a location near the bottom of said high-pressure stage, subjecting said portion to an expansion inwhich energy is lost mechanically and feeding the expanded air to about the middle of the low-pressure stage of the air separator.

References Cited in the file of this patent UNITED STATES PATENTS 1,521,115 Mewes et a1. Dec. 30, 1924 1,607,322 Van Nuys Nov. 16, 1926 2,503,939 De Baufre Apr. 11, 1950 

1. A PROCESS FOR THE PRODUCTION OF LIQUID OXYGEN BY SEPARATION FROM AIR, COMPRISING THE STEPS OF COMPRESSING THE AIR TO A UNIFORM PRESSURE OF ABOUT 5 TO 6 ATMOSPHERES, COOLING THE COMPRESSED AIR IN AIR REGENERATORS IN HEATEXCHANGE WITH NITROGEN COOLANT PRODUCED IN THE AIR SEPARATION, SEPARATING THEAIR INTO OXYGEN AND NITROGEN IN A TWO-STAGE AIR SEPARATOR, EXTRACTING NITROGEN AT ABOUT 5 ATMOSPHERES PRESSURE FROM THE TOP END OF THE HIGH-PRESSURE STAGE OF THE SEPARATOR, HEATING THE EXTRACTED NITROGEN IN SAID AIR REGENERATORS IN HEAT-EXCHANGE WITH THE AIR PASSING THROUGH THE LATTER, FURTHER COMPRESSING THE HEATED NITROGEN IN A NITROGEN COMPRESSOR TO A PRESSURE OF ABOUT 16 TO 30 ATMOSPHERES, COOLING THE HIGH-EXCHANGES WITH COLD EXNITROGEN REGENERATORS IN HEAT-EXCHANGE WITH COLD, EXPANDED NITROGEN, BRANCHING OFF A PORTION OF THES COOLED HIGH-PRESSURSE NITROGEN AT AN INTERMEDIATE POSITION ON THE NITROGEN REGENERATORS, EXPANDING THE LAST-MENTIONED NITROGEN BY ALLOWING THE SAMES TO LOSE ESNERGY MECHANICALLY, TO A PRESSURE SUBSTANTIALLY EQUAL TO THAT IN SAID HIGH-PRESSURE STAGE, THEREBY TO OBTAIN SAID COOLED, EXPANDED NITROGEN REHEATING THE COOLED, EXPANDED NITROGEN IN THE NITROGENL REGENERATORS, AND THEREAFTER DRAWING THE LATTER BACK INTO THE NITROGEN COMPRESSOR TO BE RECIRCULATED, SUPER-COOLING THE MORE HIGHLY COOLED REMAINDER OF THE NITROGEN LEAVING SAID NITROGEN REGENERATORS IN HEAT-EXCHANGE WITH SAID COLD, EXPANDED NITROGEN AND SUPPLYING THE SUPERCOOLED NITROGEN TO THE LOW-PRESSURE STAGE OF THE AIR-SEPARATOR AT A LOCATION NEAR TO THE TOP THEREOF, EXTRACTING SAID NITROGEN COOLANT FROM TH TOP OF SAID LOW-PRESSURE STAGE, AND EXTRACTING SUBSTANTIALLY PURE OXYGEN FROM THE BOTTOM OF THE LATTER STAGE. 